1. Field of the Invention
The invention relates to a control apparatus and method wherein supply of fuel to an engine may be stopped even in a traveling state of the vehicle.
2. Description of the Related Art
As a drive source for driving a vehicle, a hybrid vehicle equipped with an engine and a motor having a regenerative function is known from Japanese Patent Application Laid-Open No. 5-229351. In such a vehicle, with a view to improving fuel consumption, supply of fuel to an engine is stopped (fuel cut) during deceleration of the vehicle.
During deceleration, a throttle valve (a valve for adjusting an amount of intake air) is generally completely closed. Thus, if supply of fuel to the engine is stopped in this state, pistons in the engine reciprocate within an enclosed space. Reciprocating movement of the pistons offers resistance against the traveling of the vehicle. As a result, regenerative efficiency of the motor decreases and fuel consumption deteriorates. This problem arises especially in a vehicle constructed such that rotation of an engine continues during the traveling of the vehicle even if fuel supply has been stopped. Even in a vehicle constructed such that an engine can be stopped independently of the traveling of the vehicle, a similar problem arises from a timing when fuel supply is stopped to a timing when the engine is actually controlled to be stopped.
Japanese Patent Application Laid-Open No. 9-284916 discloses that outside air can be introduced by completely opening a throttle valve if supply of fuel is stopped during deceleration (regeneration) of a hybrid vehicle and wherein pumping loss of the engine is thereby reduced to the extent of improving fuel consumption. However, since the throttle valve is completely opened, a large amount of cold outside air flows into the exhaust system through the engine. Therefore, the temperature of a catalyst provided in the exhaust system decreases and causes a problem of an increase in concentrations of exhaust emission substances.
In order to solve this problem, Japanese Patent Application Laid-Open No. 11-93723 discloses that a throttle valve is almost completely opened and an exhaust gas recirculation control valve (an EGR valve) is completely opened at the same time. However, this solution can only be applied to a vehicle employing an exhaust gas recirculation control (EGR control) system, and others are simply designed to prevent cold outside air from entering an exhaust system. Thus, when the exhaust system is sufficiently warm, for example, immediately after long-term operation accompanied by fuel supply, or when outside air to be introduced is at a high temperature because of the summer season, flow of air may be excessively restricted in connection with pumping loss. The art mentioned above does not provide an effective countermeasure.
The invention solves the problems described above. According to an exemplary embodiment of the invention, a control apparatus for a motor vehicle can reliably prevent concentrations of exhaust emission substances from increasing due to a decrease in temperature of a catalyst in an exhaust system while minimizing pumping loss of an engine.
A control apparatus for a motor vehicle according to a first exemplary embodiment of the invention is constructed such that supply of fuel to an engine can be stopped even when the vehicle speed is not equal to zero. The control apparatus includes a fuel supply detector that detects whether or not supply of fuel to an engine has been stopped during a traveling state of the vehicle, a temperature detector that detects a temperature of a catalyst in an exhaust system, and a controller that restricts flow of outside air into the exhaust system if it is detected that fuel supply in the vehicle has been stopped and that the temperature of the catalyst in the exhaust system is equal to or lower than a predetermined temperature and that causes outside air to flow into the exhaust system if it is detected that fuel supply in the vehicle has been stopped and the catalyst temperature is higher than the predetermined temperature.
According to the first exemplary embodiment, when the temperature of the catalyst in the exhaust system is low, flow of outside air into the exhaust system is restricted to prevent an increase in concentrations of exhaust emission substances. On the other hand, when the catalyst temperature is high, outside air is caused to flow into the exhaust system. Thereby it becomes possible to reduce pumping loss of the engine without adversely affecting concentrations of exhaust emission substances.
Although the catalyst temperature may directly be detected, it may also be detected indirectly by detecting a temperature of a specific portion of the exhaust system.
The invention may be constructed such that an amount of intake air in the engine is increased, for example, if it is detected that fuel supply in the vehicle has been stopped and that the temperature of the catalyst in the exhaust system is equal to or higher than a predetermined temperature.
According to this construction, the amount of intake air is increased during stop of fuel supply (even if the accelerator pedal is completely closed). Therefore, air is allowed to flow around pistons of the engine, and pumping loss can be reduced correspondingly. Consequently, it becomes possible to improve fuel consumption and regenerative efficiency.
If it is detected that the catalyst temperature has become equal to or lower than a predetermined temperature, the increase in amount of intake air is stopped. Thus, even if the catalyst has been cooled through introduction of outside air, the temperature does not decrease to the extent of hampering the catalytic function. Therefore, it is possible to prevent an increase in concentrations of exhaust emission substances. In other words, since the maximum amount of intake air can be increased based on an actual temperature of the catalyst as long as the catalytic function is not hampered, it is possible to prevent both deterioration of the catalytic function and an increase of pumping loss.
Alternatively, it is possible to adopt a construction wherein the amount of intake air is increased in accordance with a temperature of the catalyst in the exhaust system if fuel supply in the vehicle has been stopped.
According to this construction, since the amount of intake air is increased depending on an actual temperature of the catalyst in the exhaust system, it is possible to more precisely realize both reduction of concentrations of exhaust emission substances of the engine and reduction of pumping loss.
The methods by which the amount of intake air is increased in accordance with an actual temperature of the catalyst may include adjusting the ratio between an open-period and a closed-period of the throttle valve for adjusting an amount of intake air depending on a temperature of the catalyst in the exhaust system or maintaining the throttle valve at a predetermined opening degree depending on a temperature of the catalyst in the throttle valve. In the latter method, wherein the throttle valve is maintained at a predetermined opening degree, there is no abrupt change in friction. Thus, the latter method is advantageous in that there is no possibility of a shock or the like being generated.
Furthermore, it is also possible to adopt a construction wherein if it is detected that fuel supply in the vehicle has been stopped, the amount of intake air in the engine is increased and exhaust valves are driven in their closing directions in accordance with a temperature of the catalyst in the exhaust system.
In this construction, while reducing pumping loss of the engine by increasing an amount of intake air in the engine, the exhaust valves of the engine are kept closed in accordance with a temperature of the catalyst in the exhaust system so as to prevent cold outside air from entering the exhaust system due to an increase in amount of intake air. Therefore, it is possible to minimize pumping loss and reliably prevent a fall in temperature of the catalyst in the exhaust system.
A control apparatus for a motor vehicle according to a second exemplary embodiment of the invention includes a fuel supply detector that detects whether or not fuel supply in the vehicle has been stopped during the traveling state of the vehicle, and a controller that increases an amount of intake air in an engine if it is detected that fuel supply in the vehicle has been stopped and that retards a timing for closing exhaust valves of the engine with respect to a timing during fuel supply.
According to this embodiment, cold outside air is unlikely to enter the exhaust system including the combustion chamber. This makes it possible to prevent concentrations of exhaust emission substances from increasing due to the excessive cooling of the catalyst. In this embodiment, the amount of intake air to be introduced may be adjusted depending on an actual temperature of the catalyst.
In performing control for closing exhaust valves of the engine or control of timings for closing them, it is not necessary to control intake valves. Because the amount of intake air has been increased, the intake valves do not undergo a serious problem. However, in the case where a mechanism capable of controlling the opening and closing of the intake valves and timings for opening and closing them is provided (in many cases, a system having a mechanism for controlling exhaust valves also has a mechanism for controlling intake valves), if the intake valves are controlled to be opened (in their opening directions), pumping loss can further be suppressed.
A control method for a motor vehicle according to another exemplary embodiment of the invention includes the steps of detecting whether or not fuel supply to the engine has been stopped during a traveling state of the vehicle, detecting a temperature of a catalyst in an exhaust system, restricting flow of outside air into the exhaust system if it is detected that fuel supply in the vehicle has been stopped and that the temperature of the catalyst in the exhaust system is equal to or lower than a predetermined temperature, and permitting flow of outside air into the exhaust system if it is detected that fuel supply in the vehicle has been stopped and that the temperature of the catalyst in the exhaust system is higher than the predetermined temperature. The control method of this embodiment makes it possible to reduce pumping loss of the engine without adversely affecting concentrations of exhaust emission substances.
A control method for a motor vehicle according to another exemplary embodiment of the invention includes detecting whether or not fuel supply in the vehicle has been stopped during the traveling state of the vehicle, increasing an amount of intake air in the engine if it is detected that fuel supply in the vehicle has been stopped, and retarding a timing for losing exhaust valves of the engine with respect to a timing during fuel supply. According to this aspect, since cold outside air is unlikely to enter the exhaust system, including combustion chambers, it is possible to prevent concentrations of exhaust emission substances from increasing due to the excessive cooling of the catalyst.